Acyl coenzyme A: cholesterol acyl transferase (ACAT) is an intracellular enzyme that catalyses the formation of cholesteryl esters (CE). It has been postulated that this enzyme is responsible for the synthesis of CE in macrophages (in the artery wall), for cholesterol absorption, hepatic VLDL production and adrenal steroidogenesis. In order to determine the role of ACAT in these processes, the PI has developed ACAT knockout mice. These mice will be used to determine ACATs role in these processes. These same mice will be studied alone or after breeding with other knockout mice (apoE or LDL Receptor) and will be used to determine whether ACAT has an important role in atherosclerosis. The PI will also characterize cDNAs that appear to encode two new novel ACAT genes.